Motion-picture projector



Oct. 21, 1947. J M L R 2,429,364

MOTION-PICTURE PROJECTOR Filed April 14, 1947 2 Sheets-Sheet 1 n n-" w. In

IN V EN TOR.

PA YMo/vb J N/L L 52 BY QrW-5. QM

ATTORNEY.

Oct. 21 1941 R. MI v 2,429,364

MOTION-PICTURE PROJEGTOR Filed April 14, 1947 2 Sheets-Sheet 2 INVENTOR. 56 '64 YMOND J/V/LLEQ ATTOENE'X Patented Oct. 21, 1947 UNITED STATES PATENT OFFICE MOTION-PICTURE PROJECTOR Raymond J. Miller, Detroit, Mich.

Application April 14, 1947, Serial No. 741,259

8 Claims. 1

This invention relates to motion picture projectors and more particularly to an improved projector having means preventing objectionable overheating of the projector, particularly in the locality of the aperture plate, as Well as overheating of the film. The present application is a continuation-impart of my co-pending application Serial No. 379,962 filed February 21, 1941, the latter application being a continuation-inpart of .my prior application Serial No. 250,310 filed January 11, 1939, and now U. S. Letters Patent No. 2,312,663 granted to me on March 2, 1943.

Construction of modern motion picture projectors with respect to incorporation therein of means preventing overheating of such projectors in operation is governed by severai mutually conflicting requirements presenting an extremely difficult problem. One of such requirements is a very high intensity of illumination required on the projection screen which, usually being of a relatively large size reaching in some instances the size of 3,500 square feet, requires very powerful light source to provide required unit illumination for such a large area. At the present time electric are light is considered to be the only adequate light source .for such intensive illumination. It should be understood that all the light that reaches the screen and is dispersed over its entire area has to pass through the film aperture, which aperture is of a fixed size and .is less than one-half of one square inch in area. Thus the light concentration required at the aperture plate may be nearly 750,000 times that required at the screen. The beam of such a concentrated light, which may be compared. for the purposes of description to a beam of sunlight focused at nearly a point by a large lens, is passed through the film made of highly inflammable material, usually cellulose nitrate. Even a small fraction of a second of exposure of the film to'such light concentration would ignite the film, causing violent combustion of theentire reel andpossibly afire of serious proportions. Due .to the constantly present possibility of panic in the audience, occurrence of a fire in a theatre may have grave consequences irrespective of the actual size of the confiagration. The actual period of time during which the film is retained stationary in alignment with the aperture, of a present day projector is only .approximatel /48. of one second; increasing this time eight or nine times, i. e. to approximately /a of one second may cause instant overheating and inflammation of the film. In order to prevent such an increase of time of film exposure to the light beam, safety fire shutters are now required by law in motion picture projectors used for demonstrations to public audiences, which Safety fire shutters are actuated by centrifugal type governors to close and to interrupt the light when the speed of the film falls down to a predetermined limit.

While the high speed of the film motion and presence of the safety fire shutter take care of the danger from the light which is passed actually through the film, there remains a large portion of intense light of extremely high heating value which does not pass through but falls on portions of the projector structure, constantly imparting to it large quantities of heat in the immediate locality of the film aperture. It is clear that unless this heat is dissipated, the temperature of the projector in the locality of the aperture plate will rise very'quickly and the heat will be passed to the aperture plate raising its temperature to the point when treating the film, i. e. operatively arranging it by hand at the aperture plate in engagement with driving means, will become very difiicult, and upon further operation of the projector making possibleinfiammation of the film by contact with the hot aperture plate. This heat may be considered herein in two of its main portions, namely, the portion of the heat that is imparted to the rotating shutter operating to interrupt the light while the film is being moved, and the portion which passes the shutter but is imparted to the structure of the projector structure immediately surrounding the profiling apertures of the projector; the latter portion of the heat is often referred to as spillage light heat.

The rotating shutter operating in the path of the light absorbs a considerable portion of the heat of projected light during the entire cycle, as well as all of the heat during the time when it interrupts the light, whichis approximately 20% of the cycle time. Unless the shutter is cooled, its temperature will rise beyond permissible temperature, bringing about overheating of the projector.

As to the heat of the spillage light, this heat is particularly dangerous because it is imparted to the projector structure very close to the aperture plate and partly directly into it, and moreover is caused by the light of nearly maximum concentration. The light of the electric arc is reflected by a concave mirror and is directed as a converging beam of light toward the film aperture. The cross section of such a beam is approximately circular and therefore if it were projected onto the rectangular film aperture, the marginal portions of the beam outside of the area of the aperture would impart all of its heat directly into the aperture plate. To prevent such a dangerous condition, the beam i profiled prior to its reaching the aperture plate to have a rectangular cross section, in order to reduce by such an expedient the marginal areas of the aperture plate receiving the spillage light of full concentration and of high heating intensity. The final profiling of the picture frame is done at the aperture plate, with the film running on aperture plate tracks with a very small clearance, such as approximately .010 of an inch, from the aperture piece in which the profiling aperture is provided.

The preliminary profiling is done at the light port or a similar opening provided in a suitable member interposed in the path of the projected light. Provision of such a member introduced a number of serious difliculties. First of all, there is a problem of removal of heat from such a member. It can be appreciated in view of the foregoing that unless this is done, such a member will soon be heated to nearly red heat and the heat imparted thereto will be transferred, in part at least, to the aperture plate. The second difficulty results from the tendency of the air to flow through the light port, thus forming air currents which have been found very objectionable, particularly if directed into electric arc compartment. Air flow into the arc compartment was found to produce flickering and wandering of the arc, noticeable on the screen. The flow of air from the arc compartment toward the film has been found also objectionable, since this air is very hot and carries with it incandescent and very abrasive arc ashes, usually sodium silicate which is one of the products of combustion of the electrodes, which ashes are very injurious to the film and the delicate film-actuating mechanisms.

Many attempts have been made to solve these difiiculties. Removal of the heat from the profiling member was attempted by surrounding it with a water jacket and circulating water therethrough. Such means introduced other complications into the construction and use of the projectors. It was also attempted to laminate such a profiling member and to blow the air under considerable pressure through the laminations. Such expedients produced the danger of blowing into the arc compartment and producing the undesir able interference with the arc. Moreover, the use of independent blowing means made these expedients rather unreliable, since failure of the blower or mistake of the operator could cause the projector to operate with stalled cooling system. Flow of the air through the light port was attempted to be prevented by closing this port with the aid of a lens means termed condenser lens. While being successful in preventing the fiow of air into the arc compartment, such means materially reduced intensity of illumination, and have been considered undesirable for this and other reasons.

One of the objects of the present invention is to provide an improved motion picture projector in which the above difiiculties are overcome and largely eliminated with the aid of simple and inexpensive means.

Another object of the invention is to provide an improved motion picture projector having an aperture plate or a similar member contacted by the film, in which plate or member there is effected such a heat balance that equilibrium of the quantities of heat imparted to that member and dissipated thereby is reached at a desirably low temperature, such for instance as at a temperature not to high for touching such member with the hand.

Another object of the invention is to provide an improved motion picture projector having an aperture plate or a similar member contacted by the film, in which projector there are provided means whereby a substantial portion of the heat of the projection light beam which otherwise would be imparted to the aperture plate and the film, and particularly the heat of the spillage light, is intercepted before it reaches the aperture plate, and is carried away into the atmosphere.

A further object of the invention is to provide an improved motion picture projector of the character specified in the preceding paragraph, in which projector there are provided means operating to remove from the aperture plate or an equivalent member the heat which passes through the above mentioned heat intercepting means and is imparted to the aperture plate, said means operating also to cool the light beam itself by providing a medium absorbing from the light beam a portion of rays having high heating value, and furthermore to provide a layer of cool clean air immediately adjacent the film to protect it from the incandescent abrasive ashes which may be carried by the air flowing through the open light port toward the film.

A still further object of the invention is to provide an improved motion picture projector in which the undesirable flow of the air from the arc compartment toward the film is controlled and is held at such an intensity that its injurious tendencies remain within the protective capacity of the means specified in the preceding paragraph.

A still further object of the invention is to provide an improved projector adapted to utilize an electric are light and having an open light port, means being provided to prevent the flow of air into the arc compartment and the resulting interference with the arc.

A still further object of the invention is to provide an improved motion picture projector of the above character, having means whereby the heat imparted to the light-interrupting shutter is removed therefrom at a rate ensuring that the temperature of the shutter does not rise above a predetermined limit even in a prolonged operation of the projector.

A still further object of the present invention is to provide an improved motion picture projector of the foregoing character, in which projector cooling is effected by means of a convection air current, and particularly by circulation of atmospheric air through the projector with the aid of blower means operating to create a partial vacuum, rather than pressure, in the locality of the film, said blower means being furthermore driven by the film-actuating mechanism, whereby starting of the projector and bringing the film to the speed where the safety fire shutter opens is accompanied or results also in operation of the blower means.

It is a further object of the present invention to provide an improved motion picture projector having a cooling system of the foregoing character, which system is simple and rugged in construction, safe and dependable in operation, and which is relatively inexpensive to manufacture.

Other objects and advantages of this invention will be apparent from the following detailed des'oription considered Iin connection with the faccompanymg drawings, submitted ffor purposes of illustration tonly, and :not intended to define the scope of the invention, reference being :had :for that purpose to the "subjoi ned claims.

In the drawings wherein isimilar referenbe'characters refer to similar parts throughout the several views:

Fig. 1 is a perspective view partly in :section of a-moti'on picture projectonem'bodying the present invention.

Fig. :2 is a plain view partly in section of =a;portion of the projector illustrated in .1.

Fig. 3 is a section view taken substantially the line 3--3 of Fig. 52, flocking :in the direction of the arrows.

Fig. 4 is a sectional view taken substantially on the line "4- 4 of Fig. 2, locking :in the direction of the arrows.

Before explaining in detail the present invention it is to be understood that the invention :is not limited in its application to the details of construction and varrangernen-tof parts illustrated in the accompanying drawings, since the fin-vention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to .be understood that the gphraseolog-y :or terminology employed herein is ior the purpose of description and not of limitation.

Referring to Fig. 1, it will -be-observed that the invention is illustrated as being embodied in ?a motion picture .projector wherein a plurality of separate visual images are carried by a strip of celluloid or other suitable film material to. In one form of projector used commercially in theaters, the film i0 .is approximately thirty-five millimeters in width, and the separate images are carried 'by a plurality of substantially equally spaced successive -frames. Where the thirty-five millimeter (film is employed it Jhas been f-ound that very desirable results are obtained where sixteen separate 'frames are provided in a foot of film.

Means such for example as an intermittently driven sprdcke't "may be provided to intermittently move the film Ill between up'perandlower 'feed sprockets l2 and T4 to intermittently position succeeding frames of the film into alignment withan aperture T6 L'formed'in an aperturejp'late 'l'8. Light'irom a suitable source,,lparticularly an electricjarc, is directedtoimpinge on the aperture plate 18 and pass through the aperture I 6 and the film Ill to project "the image 'from the film onto a screen so positioned as for example in a theater, to be Viewed.

In the thirty-five millimeter film generally used Lfer commercial projection the r-film i0 .is provided adjacent each frame with-four sprocket receiving apertures or holes 30 to -recei-ve sprocket teethZZ 'extending'radially attheouter edges if the driving sprockets i2 and i4 and an intermittently di iven sprocket whereby "the :Yiilm Ill may be moved to position successive frames of film'into alignment "with the aperture It. Each ,of the film driving sprockets ispreferably provided With sixteendriving teeth 22 oneach side and thus moves four frames-of the film in one complete revolution.

The film may move at any predetermined speed. 7

6 that is, at the rate of tone a'nd one-shalt feet or 24 frames per second.

To drive the :fi'lm at this speed the intermittence drive sprocket must be actuated 14.40 times per minute, "making :9, quarter revolution each time it is actuated, and the upper and lower feed sprockets 12 and 14 must be continuously di-iveniataspeediof :360?R,P.LM.

One complete revolution of the intermittently driven sproclcet will move four frames, and since this sprocket makes :six complete revolutions 'per second, it Emust be :actuated through :a complete cycle each. ii 24 of :a second. This cycle must be further subdivided since an interval :of time iis required to move the film. Good results have been :obtaineii where this cycle is divided into five eduaily spaced time intervals of of a second each. One of these time intervals of V120 of :a second may be utilized to actuate the intermittently driven sprocket to position the next succeeding :frame "of the film in alignment with the aperture lit, and each individual iframe may be maintained in alignment with the aperture the remaining 4/120 Of 5a second of each cycle of ,54 of :aZSEGOnd to :permit light from a suitable source to pass through the aperture l t and :fi-lm 10 to project'itheiimageifrom the Fiilm onto the screen.

A shutter such :for example as "a rotatable blade M is @provided to intermittently interrupt the flow 10f flight "through the rfilm I0 and aperture it to ip'revent :the images on the screen from becoming blurred ior streakedras the intermittently driven sprocket moves successive ":frames :of the film +0 =into alignment withtheaperture 5| 6. Who shutter :blade again puts the light substantially 13'80 later toipreveiit visible flicker.

:Each of "the frames of the ifilm is subjected :to the run :heat intensity of the ,rprojec'tin'g blight during the interval of time "when it is aligned with the aperture 46 when the shutter blade '24 is not interrupting the :projecting light to pre- "vent ivisibl'elfl-icker or to shield movement of the illm. Each frame or the :film is therefore sub- :jected directly to the heat of the :light for lapproximately 4 :of a second while :it :is aligned with the aperture t5, and in addition is subj ented to heat conducted *to it through :the :aperture plate 48. In view'of ithe a'aot that the film i0 is made of inflammable material, a 'consider- .able-fire hazard ris ithusii-n'volved.

I he component elements of the projector may be carried by a main housing 26 having trout and back walls F28 and 30 respectively and' an intermediate wall 32 dividing the space within the housing 25 into transversely spaced mechanism and film compartments and "36 respectively.

The mechanism required to drive the film sprockets l2 and M, the intermittently driven film feeding sprocket, and the shutter 24 may be positioned within the ;mechanism compartment .34. Flihe driving mechanismpreferably includes a-generally vertically extendingdriveshaft B8 "operably connected to drive generally horizontally extending shafts projecting through and suitably sealed in the ntermediate wall 32 to prevent the escape of lubricating oil from the compartment 54 to ltheifilm compartment .376.

A 'film track carrier lllsupports the aperture ,plate 4.8 havin the aperture it formed therein. I'Ihecarrier 30 maybe supported by an aperture .plate (housing 42 ,preferably aligned with a wall -44- projecting transversely from the wall -32,

fEhe film in is preferably guided between guide rollers 46 and moves between spaced tracks "48 and shoes 50 yieldingly urgedatowards the :tracks 48 by springs 52. The film is thus maintained in proper alignment with the aperture I6 and restrained from moving a greater distance than is desired each time the intermittently driven sprocket is actuated by the driving mechanism associated with the flywheel 54.

The projecting light may emanate from any suitable source, preferably electric arc, preferably positioned behind the back wall 36 and the light is admitted into the film compartment 36 through a conical housing 56 communicating with a. shutter housing 58 having the rotatable shutter blade 2 therein. A fire shield 66 formed of fireproof material such for example as asbestos may be interposed between the shutter housing 53 and a preferably inwardly extending bafile or light tube 62 formed in the back wall 36. The bafile or light tube 62 terminates in a light admission port 6 aligned with the aperture I6 formed in the aperture plate I8.

A fire shutter or gate 66 mounted on a suitable actuating frame 68, more fully disclosed in my co-pending application Serial No. 256,310, now U. S. Patent No. 2,312,663, issued on March 2, 1943, may be provided to automatically close the space between the aperture I6 and port 64 adjacent the baffle or light tube 62 to interrupt the flow of projecting light and heat to the film in the event that the projector fails to operate at the desired speed. A manually operated member I6 may be provided to move the fire valve 66 to the operative position illustrated in Fig. 4 when the projector is not operating.

Any desired form of shutter such for example as those disclosed in my co-pending application Serial No. 250,310, new U. S. Patent No. 2,312,663, issued on March 2, 1943, may be employed to interrupt the projecting light when the film I6 is being intermittently moved to align succeeding film frames with the aperture I6, One desirable form includes the rotatable shutter blade 24 mounted on a shaft 12 and provided with a counterbalancing weight I4. The shaft I2 projects through a suitable oil seal I6 positioned in the intermediate wall 32 and is operably connected Means are provided to withdraw heat from the projecting light and to cool the film, aperture plate and the associated parts of the projector subjected to heat during operation of the projector.

One desirable form of such cooling means comprises a blower 86 communicating directly with the atmosphere on one side, and communicating with the atmosphere on its other side by way of a manifold 82 and an aperture cooling chamber 84. The manifold passage 82 is formed by the intermediate wall 32 and the wall 44 aligned with the aperture plate housing 42, a portion of the back wall 36, and an extension 86 thereof. The aperture cooling chamber 84 is positioned between the back wall 36 and bailie or light tube 62 on one side, and the aperture plate housing 42, the film track carrier 46, and the aperture plate I8 on the other side.

The blower 86 is provided with impeller blades 88 carried by a disk 96 supporting the shutter blade 24 and the counterweight I4. The blades 88 rotate in a suitable housing 92 communicating with atmosphere on one side by way of a plurality of apertures 64, which by way of example may be discharge apertures.

Cooling air may be withdrawn from the atmosphere through inlet apertures 96 formed in the back wall 30 adjacent the vertical edge of the aperture plate housing 42 adapted to be engaged by a vertically extending portion 96 of a side door I66 to seal the film compartment 36 from the aperture cooling chamber 84.

The cooling air is thus drawn from the atmosphere through the inlet apertures 96 into the aperture cooling chamber 84 where it passes across the aperture plate housing 42, film track carrier 46 and is directed by venturi I62 carried by the film track carrier to impinge on and cool the aperture plate I8 and film I6 aligned with the aperture IS. The cooling air is then propelled through the manifold 82 to the housing 92 of the blower where it is discharged to atmosphere by the blades 88 through the apertures 94. The direction of the flow of air through the aperture cooling chamber 84, manifold 82 and blower 86 is indicated by the arrows I64.

Attention is called to the fact that the flow of cooling air is confined to the aperture cooling chamber 84 and manifold 82, and that the air within the film compartment 36 is not disturbed. The possibility of dirt entering the film compartment to injure the delicate film positioning and moving mechanism and the projector lenses is therefore minimized.

The fiow of cooling air into, out of and through the aperture cooling chamber 84 causes virtually no disturbance of air in the shutter housing 58 because the flow of air through the inlet apertures 96 across the chamber 84 to the manifold 82 is less restricted than it is through the shutter housing 58 and the light admission port 64 of the inwardly directed baffle or light tube 62. There is thus virtually no tendency for the cooling air to set up disturbing air currents which might interfere with the operation of the light source such for example as an are light.

If desired, the blower may be a separate unit not associated with the shutter mechanism, and may be positioned in any convenient location to direct cooling air through the space between the aperture plate and the shutter mechanism without departing from the spirit of my invention.

A framing light I68 preferably positioned in the aperture cooling chamber 84 may be provided to permit observation of the film I6 through an observation port positioned forwardly of the aperture plate I8 to determine whether the frames of the film are in proper alignment with the aperture I6. A switch II6 having a plunger II2 positioned to be engaged by the door I66 when in the closed position may be provided to permit the light to be illuminated when the door is open and to shut it off when the door is closed.

A glass H4 positioned in the shutter housing 58 may be provided to permit inspection of the projecting light with reference to the fire shield 66 to facilitate adjustment of the light relative to the aperture plate l8 and aperture I6.

A channel H6 formed in the back wall 36 adjacent the bafile or light tube 62 may be provided to receive a valve member whereby the projecting light may be interrupted to facilitate changing over from one projector to another when a reel of film is exhausted or for any other purpose.

I claim:

1. In a motion picture projector adapted to utilize an electric are light and to project such light along a predetermined line, an aperture plate spaced from the arc and having a film aperture, means adapted to pass a film in close proximity o said ape ture; aaa r. rcu t-l carryingawey heat. tendin o be, impar ed t the. il by: the are l h .v aid circuit comnr sips; a, cooling c amber hav n n, in akev o en n and discharg pen n communicat n irectl w th the atmosphere. said. chamber be g er-m d. part by two spac d ex nd n trans erse r to; theline o pr i eted1ish the Watt dispos d clo er o; th re havin an p P rt d osed of li nd pr v d n at predeterm n d meets a path for t e l t. fr m h ar to said a r ur entire y th ugh h a r space, he. Wal d sp ed further away rom; sai areeeine: ad *1 edtq carry said aperture, plate; a light tube provided within said chamber along the line of light, said tube having one open end connected to one of said walls, with its free open end terminating within said chamber at a distance from the. other wall; and blower means adapted to create a flow of atmospheric air through said chamber around said tube and past the free, end thereof.

2. In a motion picture projector adapted to utilize,- an electric arc lightan'd to project; such light along a predetermined line, an aperture plate spaced from the arc and having a aper ture, m a a pted to p ss afilm in 5 PM??? imity to said aperture; an air circuit for carrying away heat tending to be imparted to the film by the arc light, said circuit comprising a cooling chamber having an intake opening and a discharge opening communicating directly with the atmosphere, said chamber being formed, in part, by two spaced walls extending transversely to the line of projected light, the wall disposed closer to the are having an open port disposed in said line of light and providing at predetermined momerits a path for the light from the arc to said aperture entirely through the air space, the wall disposed further away from said arc being adapted to carry said aperture plate; a substantially tubular heat-absorbing extension provided within said chamber along the line of light, said extension having one open end connected to one of said walls, with its free open end terminating within said chamber at a distance from the other wall; and blower means adapted to create a flow of atmospheric air through said chamber around said heat-absorbing extension and past the free end thereof to carry away the heat imparted by the arc light to said extension and to provide a cooling layer of moving air across the open free end of said extension.

3. In a motion picture projector adapted to utilize an electric are light and to project such light along a predetermined line, an aperture plate spaced from said are and having a film aperture, means adapted to pass a film in close proximity to said aperture, an air circuit for carrying away a substantial portion of the heat tending to be imparted to the film by the are light, said circuit comprising a blower having one side communicating with the atmosphere, a cooling chamber having one opening communicating directly with the atmosphere and another opening communicating with said blower, said chamber being formed, in part, by two spaced walls extending transversely to the line of projected light, the wall disposed closer to the arc having an open port dis-posed along said line of light and providing at predetermined moments a path directly through air space from said are to the film, the wall disposed further away from said are being adapted to carry said aperture plate, a light tube provided within said chamber and aligned with said port and said aperture 10 he ease sees a the passage Qt li ht an wa ls di r ing and ar sa ha ng n o as: pen nds r. 1 W ll an set er 9 s. d ree nd e se, me wi h n said Q m sn said; blower adapted to create a flow of eelies a r hrough said l-tam e a e the w p r s ft th l sh lb e d e r s t e it thereof, the. now, of air across. said free,

being substantially in the plane of said end 4. A construction as defined by, the preceding new 3 th l h t b bein Q ho low. res a teda ross sec on e f u er wel s of sa d rear be forming a bade d r c in a P03 1 1 e bl nsair owa d he film,-v

lei a motio pi t e Pr e o ada t d tQ util'ze an electric arc. lightan'd to project such i h some ae ed te m eed e an t re Pl te seated. t am said a nd vi g t a s: tar mea s. a p ed o pass a fi m lose Preteens 9 sa de i li e or op ra i l e ment 02 the picturesfof said film with said apre tur a, sha t d en b the film actu imsm an an interrupting shutter mounted on said shaft nd adapt d t n e upt the l ght at pa e mmed mom n s ai 'rcuit f r, a yi g way a substantial portion of the heat tending to be imparted to the aperture plate and to the film by the are light, said circuit comprising a blower having an impeller mounted on said shaft, said blower having its discharge side communicating with the atmosphere, a cooling chamber having one opening communicating with the atmosphere and another opening communicating with said blower, said chamber being formed in part by two spaced walls extending transversely to the line of projected light, the wall disposed closer to the are having an open port disposed along said line of light and providing a path for the light, except when said path is interrupted by the shutter, directly through the air space from said are to the film, the wall disposed further away from said are being adapted to carry said aperture plate.

6. In a motion picture projector adapted to utilize an electric are light and to project such light along a predetermined line, an aperture plate spaced from said arc and having a film aperture; means adapted to pass a film in close proximity to said aperture for operative alignment of the pictures of said film with said aperture; a shaft driven by the film actuating means; an interrupting shutter mounted on said shaft and adapted to interrupt the light at predetermined moments; an air circuit for carrying away a substantial portion of the heat tending to be imparted to the aperture plate and to the film by the are light, said circuit comprising a blower having an impeller mounted on said shaft, said blower having its discharge side communicating with the atmosphere, a cooling chamber having one opening communicating with the atmosphere and another opening communicating with said blower, said chamber being formed in part by two spaced walls extending transversely tothe line of projected light, the wall disposed closer to the are having an open port disposed along said line of light and providing a, path for the light, except when said path is interrupted by the shutter, directly through the air space from said are to the film, the wall disposed further away from said arc being adapted to carry said aperture plate, a, light tube provided within said chamber and aligned with said port and said aperture and having open ends for the passage 11 of light therethrough, said tube being integrally formed on one of said chamber walls, said blower being adapted to create a fiow of cooling air through said chamber around the outer walls of said light tube and across the free end thereof.

'7. A construction as defined by the preceding claim 6, the intake opening of said chamber providing a communication thereof with the atmosphere being at least equal in area to that of the light port.

8. In a motion picture projector adapted to utilize an electric arc light and to project such light along a predetermined line, an aperture plate spaced from the arc and having a film aperture, said projector being adapted to provide at predetermined moments an unobstructed path for the are light from the arc to said film entirely through air space, means adapted to pass a film in contact with said aperture plate for registration of the film picture frames with said aperture; an air circuit for carrying away heat tending to be imparted to the film by the are light, said circuit comprising a chamber having an atmospheric intake opening and formed, in part, by two spaced walls extending transversely to the line of projected light, the wall disposed closer 12 to the are having an open port disposed on said line of light substantially perpendicular thereto, the wall disposed further away from said are being adapted to carry said aperture plate; a blower operatively interposed in said circuit, said blower having its suction side communicating with said chamber and adapted to create a flow of free atmospheric air through said chamber transversely of the line of light from said atmospheric intake opening and to discharge such air directly into the atmosphere; means for driving said blower, said means being interconnected with the film actuating means.

RAYMOND J. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,853,725 Dina Apr. 12, 1932 2,186,618 Philips Jan. 9, 1940 2,194,585 Brenkert Mar. 26, 1940 2,312,663 Miller Mar. 2, 1943 2,378,682 Brenkert June 19, 1945 

